As an additional comment to the one I just posted: There is more than one Lucille Drouin of the right age to marry your grandfather.
In the 1940 census I find a Lucille Drouin age 21 in Detroit; she's born in Canada (you say your grandmother was born in Quebec). But those parents - Henry Drouin and Yvonne - have thirteen children and it seems odd that Lucille would be adopted by them. Lucille is the oldest. She seems more like a person who could be helpful in the household, if she entered the family at an older age.
I see a Marie Jenne Lucille Drouin birth in Quebec - but probably she had a different surname at birth?